Harold G. Klemcke

Effects of estrogen-induced hyperprolactinemia on endocrine and sexual functions in adult male rats

Chronic estrogen treatment can lead to development of prolactin (PRL) secreting pituitary tumors. We have tested the ability of diethylstilbestrol (DES) to produce persistent hyperprolactinemia (hyperPRL) in adult male rats and examined the effects of this treatment on hypothalamic-pituitary-testicular function, adenohypophyseal structure, copulatory behavior and fertility. Silastic capsules containing approximately 5 mg DES were subcutaneously implanted into adult male CDF (F-344)/CrlBR rats and removed 15 or 20 weeks later. Extreme hyperPRL, as well as suppression of plasma LH and FSH levels, persisted after DES capsules were removed. In contrast, plasma testosterone levels increased rapidly after removal of DES capsules and reached normal levels within 4-6 weeks. Copulatory behavior was assessed on two occasions between 7 and 14 weeks after removal of the DES capsules and was found to be suppressed in DES-treated rats, as evidenced by significant increases in latencies to mount, to intromit and to ejaculate. Moreover, when the animals were placed with normal females, the interval until conception was significantly greater in DES-treated than in control males. In spite of these differences in copulatory behavior, 10 of 11 DES-treated males were fertile. At autopsy, 44 weeks after capsule implantation (i.e. 24 or 29 weeks after capsule removal), DES-treated rats had marked enlargement of the anterior pituitary, increased weights of the lateral prostate and the adrenals, increased levels of testicular hCG-binding sites, reduced concentration of dopamine and norepinephrine in the median eminence and increased concentration of LHRH in the preoptic area.(ABSTRACT TRUNCATED AT 250 WORDS)

Photoperiod and regulation of gonadotropin receptors.

In the overwhelming majority of animal species, reproductive functions do not continue throughout the year, but are restricted to a breeding season. With the exception of animals inhabiting the equatorial region, the highly predictable timing of onset and termination of the breeding season is related to annual changes in photoperiod (day length). Arrival of young during optimal nutritional and climatic conditions contributes in a major way to evolutionary success and, indeed, survival of a species. It is. therefore, not surprising that animals utilize the most constant and reliable of environmental clues, namely annual changes in photoperiod, to achieve synchrony of reproduction with seasonal changes in temperature, rainfall. and food availability. In most species with short gestation, the breeding season starts during increasing photoperiod and ends during decreasing photoperiod, thus ensuring birth of litters during spring and summer. Much of the current understanding of the environmental and physiological regulation of seasonal breeding patterns in this category of species is based on studies in the golden (Syrian) hamster, Mesocricetus ( i r m i t i i x . Limited information on the ecology of this species indicates that reproduction in golden hamsters in their natural habitat is restricted to spring and summer. This reproductive period is followed by gonadal involution and hibernation. Gonadal recrudescence occurs toward the end of winter and hamsters resume breeding shortly after emergence from hibernation. Whcn golden hamsters are maintained in a laboratory and exposed to natural photoperiod in temperate zones, they exhibit normal seasonal changes in gonadal activity even though they typically fail to hibernate. In animals maintained in an artificially controlled photoperiod, a predictable sequence of gonadal regression and recrudescence can be induced at any time of the year by altering the length of illumination during each 24-h period. Experiments involving exposure to brief periods of light or to alternating periods of light and dark with a total duration different from 24 hours provided evidence that photoperiod entrains circadian rhythms of photosensitivity. Hence, the presence or absence of light during specific times of the day is interpreted by the animal as ‘‘long’’ or “short” days. Variations of photoperiod can lead to stimulation, maintenancc, or suppression of gonadal function. depending on prior photoperiod conditions.‘ When one uninterrupted period of illumination occurs every 24 hours, day lengths equal to or exceeding 12.5 hours maintain reproductive competence

Interactions of Photoperiod and Ectopic Pituitary Grafts on Hypothalamic and Pituitary Function in Male Hamsters

Exposure of adult male hamsters to short days (less than 12.5 light/day) leads to suppression of gonadal function which is secondary to reductions in gonadotropin and prolactin (PRL) secretion. PRL secretion is decreased in short days despite a reduction of dopaminergic (DA) input from the hypothalamus, suggesting that the pituitary may become more sensitive to the inhibitory effects of DA. Although hypothalamic DA metabolism is altered by short-day exposure, it is not known whether the DA system can respond to PRL feedback or whether these changes in DA or PRL levels are responsible for the observed changes in gonadotropin secretion. To address these questions, the effects of PRL-secreting ectopic pituitary grafts on hypothalamic catecholamine metabolism and the effects of experimental manipulations of catecholamine metabolism on PRL and gonadotropin secretion were evaluated in adult male hamsters exposed to a 14 h light: 10 h dark (14L:10D) or a 5L:19D photoperiod. Short-photoperiod exposure led to expected reductions in testes weight, plasma PRL levels, and in vitro PRL secretion, but circulating levels of luteinizing hormone or follicle-stimulating hormone were not affected. Norepinephrine and DA turnover in the median eminence and in the medial basal hypothalamus was also reduced in the 5L:19D as compared to the 14L:10D animals. Pituitary grafts elevated PRL levels and hypothalamic DA turnover in animals from either photoperiod, but in vitro PRL secretion was reduced only from the pituitaries of 14L:10D hamsters. Short-photoperiod exposure increased the ability of DA to suppress PRL secretion, and this effect could be reversed by the presence of an ectopic pituitary graft.(ABSTRACT TRUNCATED AT 250 WORDS)